In automotive air conditioning systems, the amount of refrigerant flowing through the compressor is dependent upon the cooling load on the evaporator. At low loads the thermostatic expansion valve does not pass enough refrigerant to feed back to the compressor to cool and lubricate the compressor. Under these conditions, it is necessary to by-pass the evaporator and feed more refrigerant back to the compressor to prevent it from overheating. The by-pass valve presently used in automotive air conditioning systems comprises a simple check valve substantially the same as a tire valve of the Shrader type. This valve opens at low pressure differential and remains open thereafter. Therefore, under high evaporator load (high cooling load) conditions, the pressure relief valve is still open and by-passing refrigerant back to the compressor. This means that the compressor is doing needless extra work and wasting energy.